Press Association have reported that the 95-year-old monarch is staying at her Windsor Castle home after being advised by doctors to rest.
The Queen reluctantly had to cancel a trip to Northern Ireland on Wednesday on doctors advice that she rest after a busy schedule.
Boris Johnson commented on the Queen during a visit to a vaccine centre in west London on Friday, saying: “I think everybody sends Her Majesty our very, very best wishes. And certainly we have from the Government.
“But I’m given to understand that actually Her Majesty is characteristically back at her desk at Windsor as we speak. But we send her every possible good wish.”
A source previously said the Queen is “resting and undertaking light duties”.
Her brief stay at King Edward VII’s hospital on Wednesday was for “preliminary investigations”, and was kept a secret by Buckingham Palace.
It is understood the Queen was due to stay for only a short period while seen by specialists, so the development was not announced by the Palace at the time, and protecting her medical privacy was also a consideration.
The overnight admittance was for “practical reasons”, a source said.
Buckingham Palace issues statement after Queen spends the night in hospital
A Buckingham Palace spokesman said late on Thursday night: “Following medical advice to rest for a few days, the Queen attended hospital on Wednesday afternoon for some preliminary investigations, returning to Windsor Castle at lunchtime today, and remains in good spirits.”
Joe Little, managing editor of Majesty Magazine, said the issue of revealing details about the monarch’s health is problematic: “This is a tricky one because the Queen does have a right to a certain degree of privacy, but on the other hand she’s head of state.
“So does that entitle us to know exactly what ailments she may or may not have? It’s a very difficult one to get the balance right for the satisfaction of everybody.”
A statement released by Buckingham Palace on Wednesday at 11am, before the Queen was admitted to hospital that afternoon, announced the cancellation of her two-day visit to Northern Ireland.
It read: “The Queen has reluctantly accepted medical advice to rest for the next few days”, and went to say she was “disappointed” at not being able to travel and sent her “warmest good wishes” to the people of Northern Ireland.